Types of Water Contaminants
Is tap water really safe for drinking? Well, that is a controversial question. The truth is that municipalities do their best to ensure that they provide clean water. Unfortunately, the water they deliver is not clean enough. With a Reverse Osmosis (RO) system in place you can be certain that the water you drink is free of most types of contaminants.
The process of reverse osmosis involves water being filtered through a semi-permeable membrane (see our page for additional information about how a RO filter works). A typical RO system has four filters (the sediment filter, carbon filter, the reverse osmosis filter, and the post carbon filter). Each filter is responsible for removing certain types of contaminants.
Types of water contaminants
Generally, RO systems get rid of contaminants such as viruses, bacteria, protozoa and chemicals. The list below shows the types of chemicals removed and the percentage of effectiveness of the system in their removal.
| Contaminant | % of removal | Contaminant | % of removal |
| Aluminum | 97-98% | Nickel | 97-99% |
| Ammonium | 85-95% | Nitrate | 93-96% |
| Arsenic | 94-96% | Phosphate | 99+% |
| Bacteria | 99+% | Polyphosphate | 98%-99% |
| Bicarbonate | 95-96% | Potassium | 92% |
| Boron | 50-70% | Pyrogen | 99+% |
| Bromide | 93-96% | Radioactivity | 95-98% |
| Cadmium | 96-98% | Radium | 97% |
| Calcium | 96-98% | Selenium | 97% |
| Chloride | 94-95% | Silica | 85-90% |
| Chromate | 90-98% | Silicate | 95-97% |
| Chromium | 96-98% | Silver | 95-97% |
| Copper | 97-99% | Sodium | 92-98% |
| Cyanide | 90-95% | Sulphate | 96-98% |
| Ferro cyanide | 98-99% | Sulphite | 96-98% |
| Iron | 98-99% | Zinc | 98-99% |
| Lead | 96-98% | Insecticides | 97% |
| Magnesium | 96-98% | Detergents | 97% |
| Manganese | 96-98% | Herbicides | 97% |
| Mercury | 96-98% | Virus | 99+% |
| Total Dissolved Solids TDS | 95-99% | Hardness | 93-97% |
The percentages indicated above are generally accepted in the industry. However, an RO system could perform better or worse than the figures noted above because other factors could affect the filtration process. Such factors include the PH, temperature, pressure and chemicals in the water. The above chart is handy for comparing the Consumer Confidence Report that details what’s in your water to potential pollutants.
The filtration process
Reverse Osmosis is primarily based on the physical process of filtration. Filtration occurs when matter (gas, liquid or solid), passes through the pores of a medium or an absorbent material. Where water contaminants are concerned, filtration is dependent on the size of contaminant, and where applicable, its charge. To increase the effectiveness of the RO filters, pretreatment of drinking water may be necessary. The pretreatment might involve adjusting the pH, adding coagulants in the water or altering the chlorine levels.
There are three types of filtration described by the CDC and understanding them will give you a clearer idea of how a good water filtration system works.
- Water first goes through the microfiltration to remove large particles that would otherwise destroy delicate filters such as the RO membrane.
- The 2nd stage is ultrafiltration to trap larger chemicals, bacteria and protozoa. In many systems, there may be 2 of these filters.
- The last filtration stage is nanofiltration or Reverse Osmosis (of these 2 choices, reverse osmosis is better) which gets rid of most chemicals to produce safe drinking water.
1. Microfiltration
Microfiltration filters have a pore size of about 0.1 microns. Some microfiltration filters have a pore size as small as 0.05 microns while others have a pore as big as 5 microns. Due to the pore size, microfiltration is effective in removing some contaminates as show below:
- Yes – Filter is effective in removing protozoa such as Giardia and Cryptosporidium
- Maybe – Filter is moderately effective at removing bacteria such as E. Coli and Salmonella
- No – Filter is not effective at removing viruses such as Rotavirus or Hepatitus A.
- No – Filter is not effective at removing chemicals
2. Ultrafiltration
Ultrafiltration filters have a pore size of about 0.003 microns with a range from 0.003 on the lower scale to 0.05 on the upper scale. The Molecular Weight Cut Off (MWCO) on these filters is between 13,000 and 200,000 Daltons. In the RO system, the ultrafiltration filter is the carbon filter.
- Yes – Filter is effective in removing protozoa such as Giardia and Cryptosporidium
- Yes – Filter is effective in removing bacteria such as E. Coli, Salmonella, and Shigella.
- Maybe – Filter is moderately effective at removing viruses such as Rotavirus and Hepatitus A.
- No – Filter is not effective at removing chemicals
3. Nanofiltration
Nanofiltration filters have even smaller pores with pore sizes between 0.001 microns and 0.01 micron. The MWCO of these filters is between 200 and 2,000 Daltons. Like the ultrafiltration filters, the effectiveness of nanofilters is affected by the size of particles, the weight, and the charge. Nanofilters aren’t typically used in a RO filter because the even smaller pores of the Reverse Osmosis membrane are used.
- Yes – Filter is effective in removing protozoa such as Giardia and Cryptosporidium
- Yes – Filter is effective in removing bacteria such as E. Coli, Salmonella, and Shigella.
- Yes – Filter is effective at removing viruses such as Rotavirus and Hepatitus A.
- Maybe – Filter is moderately effective at removing chemicals such as metal ions of copper, chromium, or lead.
4. Reverse Osmosis Membrane
Reverse Osmosis membrane filters have the smallest pores at about 0.0001 micron or 0.1nm. These filters are best at filtering out ions and molecules that the other filters can’t. In the RO system, the RO membrane filter is the last stage and filters out the smallest particles.
- Yes – Filter is effective in removing protozoa such as Giardia and Cryptosporidium
- Yes – Filter is effective in removing bacteria such as E. Coli, Salmonella, and Shigella.
- Yes – Filter is effective at removing viruses such as Rotavirus and Hepatitus A.
- Yes – Filter is effective at removing chemicals such as chromium, copper, sodium, and lead.
Conclusion
RO systems are cheap and easy to install. Also, these systems do not require lots of maintenance but they do require filter changes are regular intervals – typically every 6 months to a year depending upon the amount of contaminants in the water.
Take a look at our Reverse Osmosis Filter Reviews page to see our top picks for RO Filter systems.
